Energy-Harvesting Yarn Uses Nanotubes

When I was a child and I’d complain about it getting cold, my mother would tell me to put on a sweater. It’s possible that in the near future, when children complain that their smartphone is running out of power, their mothers may give them the same advice: put on a sweater!

This may sound bizarre, but it makes sense when you consider new research from a team of scientists at the University of Texas at Dallas and Hanyang University in South Korea. Together, they have created “twistron” yarns that harvest motion energy and convert it into electricity. The yarn filaments are made from carbon nanotubes (CNTs) that are tubes of carbon atoms with walls that are just one atom thick. These tubes are 10,000 times smaller than a human hair, and are lightweight but have incredible strength. They then twisted the yarn so much that begins to coil up on itself, just as happens when you wind up a rubber band. Add an electrolyte to the surface of the yarn, and then stretch or bend it, and it generates electricity. In their experiments, they were able to create 250 Watts per kilogram of the material when stretched 30 times per second. The power is generated at rates as low as a few cycles per second up to 600 cycles per second, which makes it a versatile technology for harvesting all sorts of motion energy.

They even sewed the yarn into a shirt, and were able to generate an electrical signal that could be used to power a sensor and its controller. According to one of the researchers, the yarns “produced over 100 times higher electrical power per weight when stretched compared to other weavable fibers reported in the literature.” Just 31 milligrams of their twistron yarn could generate enough electricity to “transmit a 2-kilobyte packet of data over a 100-meter radius every 10 seconds.” They have explored other applications, such as using ocean waves to generate electricity.

While the technology is efficient and scalable, the major challenge at this point is to find ways to fabricate the material at a cost that is low enough to be practical. Even so, applications requiring little power — such as many wearable Health Tech uses — could be affordable already.